DE102016224403A1 - Catadioptric projection objective and projection exposure method - Google Patents

Abstract

A catadioptric projection objective (PO) for imaging a pattern of a mask arranged in an object field of an object surface (OS) of the projection objective into an image field arranged in the image surface (IS) of the projection objective by means of electromagnetic radiation having an operating wavelength λ <260 nm comprises a multiplicity of lenses a plurality of quartz glass lenses and at least one fluoride crystal lens and at least one concave mirror (CM). The lenses form at least one waist group (TG1, TG2) which contains a local constriction (E) of a projection beam path with a local minimum of the cross section of the projection beam path. The waist group (TG1, TG2) includes all the lenses arranged between an object-side first boundary lens (G1-1, G3-1) and an image-side second boundary lens (G1-2, G2-2). A free optical diameter of each of the lenses of the waist group (TG1, TG2) is smaller than a minimum of the free optical diameters of the first boundary lens (G1-1, G3-1) and the second boundary lens (G1-2, G3-2). The waist group (TG1, TG2) has at least one fluoride crystal lens.

Description

AREA OF APPLICATION AND PRIOR ART

The invention relates to a catadioptric projection objective for imaging a pattern of a mask arranged in an object field of an object surface of the projection objective into an image field arranged in the image surface of the projection objective by means of electromagnetic radiation having a working wavelength λ <260 nm and to a projection exposure method that can be carried out with the aid of the projection objective.

For the production of semiconductor components and other finely structured components, predominantly microlithographic projection exposure methods are used today. In this case, masks (reticles) are used, which carry the pattern of a structure to be imaged, z. B. a line pattern of a layer of a semiconductor device. A mask is positioned in a projection exposure apparatus between a lighting system and a projection lens in the region of the object surface of the projection lens and illuminated in the area of the effective object field with an illumination radiation provided by the illumination system. The radiation changed by the mask and the pattern passes through the projection lens as projection radiation, which images the pattern of the mask in the area of the effective image field optically conjugated to the effective object field onto the substrate to be exposed. The substrate normally carries a layer sensitive to the projection radiation (photoresist, photoresist).

One of the goals in the development of projection exposure equipment and its components is to lithographically produce structures of increasingly smaller dimensions on the substrate. Smaller structures lead z. B. in semiconductor devices to higher integration densities, which generally has a favorable effect on the performance of the microstructured components produced.

The size of the structures that can be generated largely depends on the resolution capability of the projection objective used and can be increased on the one hand by reducing the wavelength of the radiation used for the projection and on the other hand by increasing the image-side numerical aperture NA of the projection objective used in the process.

In the past, predominantly refractive projection lenses were used for optical lithography. In a refractive or dioptric projection objective, all optical elements which have a refractive power are refractive elements (lenses). However, in dioptric systems, the correction of elementary aberrations, such as chromatic aberration correction and field curvature correction, becomes more difficult as the numerical aperture increases and the wavelength decreases.

One approach to achieving a flat image surface and a good correction of chromatic aberrations is the use of catadioptric projection lenses that contain both refractive optical elements with refractive power, ie lenses, as well as refractive elements with refractive power, so curved mirrors. Typically, at least one concave mirror is included. While the contributions of positive power lenses and negative power lenses are in opposite directions in an optical system of total refractive power, field curvature, and chromatic aberrations, a concave mirror, like a positive lens, has positive refractive power but opposite effect to positive lens the field curvature. Moreover, concave mirrors do not introduce chromatic aberrations.

It is not easy to integrate a concave mirror into a projection lens for microlithographic projection exposure methods because it reflects the radiation back substantially in the direction from which it is incident. There are various proposals to integrate concave mirrors in an optical imaging system so that neither problems with beam vignetting nor with pupil obscuration occur.

For this purpose u. a. developed catadioptric projection lenses that use a completely out of the optical axis arranged object field (off-axis systems). The off-axis systems can be subdivided into folded systems with geometrical beam splitting by means of one or more fully reflecting planar deflecting mirrors (folding mirrors) and into the so-called "in-line systems" which are common to all optical elements, straight (unfolded) optical Have axis.

A group of catadioptric projection objectives with geometric beam splitting uses two deflecting mirrors in order to separate the partial beam path extending from the object field to the concave mirror from the partial beam path extending from the concave mirror to the field of view. Some projection lenses with Deflection mirrors consist of two consecutively connected, imaging objective parts and have a single real intermediate image between the object plane and the image plane (see, for example, FIG. US 2006/0077366 A1 ). In other types, three consecutive, imaging objective parts are present, so that exactly two real intermediate images are generated (see, for example, FIG. WO 2004/019128 A1 (corresponding US 7,362,508 B2 ) or EP 1 480 065 A2 )

The international patent application with publication number WO 2005/069055 A2 shows exemplary embodiments of catadioptric in-line systems with three successive, imaging objective parts and two concave mirrors each arranged optically away from a pupil surface.

Among other things, the catadioptric design approach makes it possible to provide projection lenses for working wavelengths of less than 260 nm with sufficiently strong correction of chromatic aberrations that do not require different lens materials for color correction (ie, correction of chromatic aberrations). In the case of projection objectives for a working wavelength of approximately 193 nm, fused silica is used in many cases for the vast majority or all of the transparent optical elements, since this material is transparent down to 193 nm and is available on a large scale with high quality. For 157 nm operating wavelength, however, mostly calcium fluoride (CaF ₂ ) is used (see, eg US 2005/0248856 A1 ), since the absorption of synthetic silica glass is already strong at this shorter DUV wavelength.

As is well known, achromatization can be achieved by the combination of a converging lens of a relatively small dispersion material and an associated dispersing lens of a relatively large dispersion second material. For example, in catadioptric projection objectives to assist in correcting chromatic aberrations, synthetic quartz lens lenses have been proposed to be combined with lenses of the crystalline fluoride material calcium fluoride. The US 2009/0316256 A1 discloses examples of the combined use of synthetic silica glass and calcium fluoride for the purpose of assisting chromatic correction.

In addition, it has also been proposed to fabricate the last lens in the immediate vicinity of the image surface, not made of synthetic quartz glass, but of calcium fluoride, which is exposed to particularly high radiation exposure, in order to avoid problems caused by radiation-induced refractive index change (eg compaction). In this case, the second material (calcium fluoride) is not used for color correction, but to improve the long-term stability of the entire projection lens. Examples of this can be found, for. B. in the EP 1 480 065 A2 or the WO 2005/069055 A2 ,

In addition to the intrinsic aberrations that may have a projection lens due to its production, aberrations may also occur during the useful life of the projection lens, in particular during operation of the projection exposure system. Such aberrations often have their cause in changes of the optical elements installed in the projection lens due to the projection radiation used in the use. For example, this projection radiation can be absorbed to some extent by the optical elements in the projection lens, the extent of the absorption u. a. depends on the material used of the optical elements, such as the lens material, the mirror material, and / or the properties of any provided anti-reflection coating or reflective coatings. The absorption of the projection radiation can lead to a heating of the optical elements, whereby a surface deformation and, in the case of refractive elements, a refractive index change can be caused directly and indirectly via thermally induced mechanical stresses in the optical elements. Refractive index changes and surface deformations in turn lead to changes in the imaging properties of the individual optical elements and thus also of the projection objective as a whole. This problem area is often treated under the keyword "lens heating".

It is commonly attempted to at least partially compensate for heat-induced aberrations or other aberrations occurring during service life by using active manipulators. Active manipulators are usually optomechanical devices that are adapted to act on the basis of appropriate control signals to individual optical elements or groups of optical elements in order to change the optical effect so that an error occurring is at least partially compensated. For this purpose, it may be provided, for example, that individual optical elements or groups of optical elements are changed and / or deformed with regard to their position.

For economic reasons, the aim is to increase the throughput of microlithographic production processes. For this purpose one tries among other things to increase the intensity of the illumination radiation ever further, so that exposure steps can be shortened. Furthermore, a tendency is recognizable, the generation Some structures may be improved by using certain illumination settings with polarized illumination (eg, dipole illumination or quadrupole illumination), wherein in the poles the intensity of the light may be significantly increased over conventional settings. These developments can help to increase the problem of heat-induced aberrations. Compensation by means of active manipulators is therefore expected to be technically more and more expensive and costly.

TASK AND SOLUTION

It is an object of the invention to provide a catadioptric projection lens that allows improved control of heat-induced aberrations over conventional catadioptric projection objectives.

To achieve this object, the invention provides a catadioptric projection objective with the features of claim 1. Furthermore, a projection exposure method having the features of claim 21 is provided. Advantageous developments are specified in the dependent claims. The wording of all claims is incorporated herein by reference.

The catadioptric projection lens has a plurality of lenses and at least one concave mirror. The lenses include quartz glass lenses, d. H. Synthetic quartz glass lenses and at least one fluoride crystal lens, d. H. at least one lens of a crystalline fluoride material. Thus, at least two different lens materials or lenses are combined from at least two different lens materials. The lenses form at least one waist group, which contains a local constriction of a projection beam path with a local minimum of the cross section of the projection beam path. The "projection beam path" contains the totality of all steel bundles emanating from object field points, which contribute to the image formation in the image field. The projection beam path is sometimes referred to as a "light tube" or "light quiver". Coming from the object plane, the cross section of the projection beam path within the waist group tapers to the local minimum and then increases again in the direction of the image plane.

The waist group includes all the lenses which are arranged between an object-side first boundary lens and an image-side second boundary lens. The border lenses are not part of the waist group, but are the lenses immediately adjacent to the waist group. The border lenses are recognizable by the fact that a free optical diameter of each of the lenses of the waist group is smaller than a minimum of the free optical diameters of the first boundary lens and the second boundary lens. Each of the boundary lenses thus has a free optical diameter which is greater than the free optical diameter of all lenses of the waist group. A boundary lens is further distinguished by the fact that its optical diameter is greater than or equal to the free diameter of that lens which is immediately adjacent to the side facing away from the waist group. The waist group has at least one fluoride crystal lens.

By complying with these conditions, it may be possible to reduce the disadvantageous effects of "lens heating" mentioned above in comparison with conventional systems from the outset by producing certain lenses, which in principle could also be made of synthetic quartz glass, from a crystalline fluoride material. It is exploited that certain suitable for the production of lenses fluoride crystal materials, such as calcium fluoride (CaF ₂ ), barium fluoride (BaF ₂ ) or lithium fluoride (LiF), with respect to Linsenerwärmung show a much more favorable behavior than comparable lenses made of synthetic quartz glass. The more favorable behavior contributes to the fact that the light absorption in calcium fluoride and comparable fluoride crystal materials at the wavelengths considered here below 260 nm, in particular in the range around 193 nm, is smaller than the light absorption in synthetic quartz glass, so that absorption-related heating is weaker in fluoride crystal materials as with synthetic quartz glass. In addition, the specific thermal conductivity of fluoride crystal materials, such as calcium fluoride, is significantly greater than the thermal conductivity of synthetic silica glass. This has the consequence, among other things, that in the case of uneven illumination of a lens, as may occur, for example, in an extreme lighting setting, the few highly stressed and thus significantly heated areas of a lens very effectively transfer their heat energy into the surrounding areas and thus into the entire lens can derive. One consequence of this is that any radiation-induced heating of a non-uniformly illuminated lens made of fluoride crystal material over the entire lens is much more homogeneous than with a quartz glass lens of the same shape under identical inhomogeneous illumination. The better heat distribution, in turn, means that the aberrations generated by lens warming in the case of fluoride crystal materials are significantly longer-wavelength and thus easier to correct than in the case of quartz glass lenses.

In addition to these advantages due to the specific choice of materials, according to the claimed invention, the fluoride crystal material is used particularly for relatively small free optical diameter lenses within at least one waist group. Such lenses are in the region of a local constriction of the projection beam path and are thus exposed to a particularly high specific radiation heat load. Here, the advantages mentioned above have a particularly strong beneficial effect. Among other things, with relatively small lenses, the heat dissipation in the lateral direction to the socket can be made particularly efficient.

The practical implementation of the new concept is facilitated in economic terms by the fact that fluoride crystal materials suitable for the production of lenses, such as calcium fluoride, with large volumes or large diameters are only available at high cost in optically acceptable quality. For the production in the diameter of relatively small lenses, however, sufficient lens material can be procured at a reasonable cost.

Possible problems due to intrinsic birefringence of fluoride crystal materials can be avoided or reduced to an insignificant extent, i.a. a. since in a waist group the beam angles of rays passing through are generally relatively small. In addition, the crystal orientation in fluoride crystal lenses can be chosen so that the effects are small. When using several fluoride crystal lenses compensation can be achieved if necessary by suitably selected mutually rotated crystal orientations ("clocking").

It is known that there exists the possibility of using, for example, calcium fluoride in combination with quartz glass lenses for the achromatization of catadioptric projection objectives. Here, the fluoride crystal material calcium fluoride acts as a crown material to the silica glass material and therefore is preferably used in positive lenses. These positive lenses are typically arranged in areas of relatively large marginal beam heights and are immediately adjacent to synthetic quartz glass negative lenses, which acts as a flint material compared to calcium fluoride. The terms "crown material" and "flint material" hereby refer to the different dispersion properties or the different Abbe numbers of the materials. In the field of optical design, materials having a relatively larger Abbe number and generally relatively less dispersion are referred to as "crown materials", while the other material, in contrast, having a relatively smaller Abbe number corresponding to a relatively higher dispersion, is often referred to as "Flint -Material "is called. If one wishes to use a lens combination of quartz glass lens and calcium fluoride lens for optical achromatization, then the lens combination is preferably used with very large optical free diameters, for example in the vicinity of the system diaphragm in an objective part close to the image plane.

In contrast, theoretically, the use of fluoride crystal materials, such as calcium fluoride, in relatively small lenses within a waist group is rather disadvantageous for achromatization. However, a possibly disadvantageous influence is rather inferior because of the relatively small edge beam heights present in the area of waist groups. The considerations indicate that using fluoride crystal materials, such as calcium fluoride, in relatively small lenses within a waist group would rather be detrimental to achromatization and would therefore be avoided if the fluoride crystal material were to be used for achromatization purposes.

Although it is possible for a waist group to have only a single fluoride crystal lens, it is preferable to provide a plurality of fluoride crystal lenses within the waist group, e.g. B. two, three, four or five.

In particular, a waist group may have at least two immediately successive fluoride crystal lenses, optionally also three or more immediately successive fluoride crystal lenses.

It has proven to be particularly advantageous if at least one negative lens of the waist group consists of a crystalline fluoride material, so that the waist group has at least one fluoride crystal lens with negative refractive power (negative fluoride crystal lens). In some embodiments, two or more contiguous negative fluoride crystal lenses are provided. For example, a waist group may include at least one biconcave negative fluoride crystalline lens so that strong negative refractive power can be provided by a fluoride crystal lens.

The first and second boundary lenses which frame the waist group on the object side and on the image side, respectively, have larger free optical diameters compared to the lenses of the waist group. At least one of the border lenses may be made of quartz glass. In particular, it may be that both the first boundary lens and the second boundary lens is a quartz glass lens. Because, inter alia, due to the relatively large free optical diameter, the area-specific radiation exposure is lower compared to smaller lenses, the advantages of quartz glass lenses over fluoride crystal lenses (eg good availability at moderate cost, good machinability) can be used here.

The first boundary lens disposed on the object side of the waist group is preferably a positive lens that has a converging effect on the penetrating radiation to converge radiation into the waist group. Preferably, the second boundary lens immediately following the waist group on the image side is also a positive lens. Among other things, it has the task of collecting the divergent radiation emerging from the waist group.

A particularly favorable beam guidance is obtained if a quartz glass lens with a (the fluoride crystal lens facing) concave exit surface is disposed immediately in front of one of the object surface next fluoride crystal lens of a waist group and / or if arranged directly behind one of the image surface next fluoride crystal lens of a waist group a quartz glass lens with a concave entrance surface is. As a result, relatively small angles of incidence (angles of the rays impinging on a lens surface relative to the surface normal at the point of impact) can be achieved at relatively large values of the edge beam angle (angle of the marginal rays measured relative to the optical axis).

A catadioptric projection objective according to the claimed invention may be designed such that at least one real intermediate image is formed between the object surface and the image surface. In order to achieve highest image-side numerical apertures in the range of NA = 0.9 or more, in particular for projection lenses for immersion lithography with the potential for numerical apertures NA> 1, it has proven to be advantageous if the projection objective has a first objective part for imaging an object field in a first real intermediate image, a second objective part for generating a second real intermediate image with the radiation coming from the first objective part and a third objective part for imaging the second real intermediate image into the image plane. Such a threefold structure with exactly two real intermediate images can be designed with geometric beam splitting and folded optical axis or even without geometric beam splitting with a single rectilinear, continuous optical axis (in-line system).

There are exemplary embodiments in which a waist group of the type mentioned is arranged at least in the first objective part. These variants can be designed such that a first pupil surface lies between the object surface and the first intermediate image, and a waist group is arranged in the first objective part such that the first pupil surface lies in the region of the waist group. The waist group may include a negative lens of fluoride crystal material, but this is not necessary and is not provided in some embodiments.

The waist group may comprise at least two contiguous optical elements of a crystalline fluoride material, for example two, three or four.

In some variants, this waist group has a substantially refraction-free transparent plate of a crystalline fluoride material disposed immediately adjacent to the first pupil surface. For example, this transparent plate may be replaceable and aspherized on one side to serve as a wavefront correcting element. The transparent plate can also be the optically active component of a controllable manipulator lying in the projection beam path, with which the wavefront of the projection radiation can optionally be dynamically changed during operation of the projection objective. The transparent plate may alternatively consist of quartz glass.

If a waist group is arranged within the third objective part, which images the second intermediate image into the image plane, an arrangement with optical distance from the pupil surface there can be advantageous. A third pupil surface may lie in the third objective part between the second intermediate image and the image surface, and a waist group in the third objective part may be arranged optically removed from the third pupil surface in such a way that between the second intermediate image and the waist group one or more synthetic quartz glass positive lenses (ie Positive quartz glass lenses) and between the waist group and the third pupil surface are also arranged one or more positive lenses of synthetic quartz glass. By this arrangement, the Petzval correction, ie the correction of the field curvature, can be positively supported.

In some embodiments, the waist group in the third lens part has two consecutive biconcave negative lenses of a crystalline fluoride material. It may be the smallest in diameter lenses of the entire third objective part.

The projection lens may have a single waist group. It is also possible for the projection objective to contain two separate waist groups in different sections of the projection beam path or in different objective parts.

In addition to one or more waist groups, the use of fluoride crystal lenses may also be useful elsewhere. According to a further development, the projection beam path has a first partial beam path extending between the object plane and the concave mirror and a second partial beam path extending between the concave mirror and the image plane, and at least one negative lens of a crystalline fluoride material is arranged in a double-penetrating region such that the first and the second Partial beam path through the negative lens lead. Due to the better thermal conductivity of the fluoride crystal material and the associated more efficient heat dissipation, the stronger lens warming to be expected due to the double radiation passage can be lower than in the case of quartz glass.

It may also be useful to deliberately not make some lenses from a fluoride crystal material. In some embodiments, the lenses include a last lens closest to the image plane that is made of synthetic quartz glass. Due to the higher refractive index of quartz glass compared to fluoride crystal materials, higher image-side numerical apertures are possible as a result.

In all embodiments it is preferred if the projection objective has more quartz glass lenses than fluoride crystal lenses. In particular, more than 60% or more than 70% of all lenses can be made of quartz glass.

The invention also relates to a projection exposure method for exposing a radiation-sensitive substrate arranged in the region of an image surface of a projection lens to at least one image of a pattern of a mask arranged in the region of an object surface of the projection lens by means of electromagnetic radiation having a working wavelength λ <260 nm. In the projection exposure method, a projection objective used according to the invention.

Preferably, in at least one exposure mode, a multipolar illumination is used, e.g. B. a dipole illumination or a quadrupole illumination.

Furthermore, the invention relates to a projection exposure apparatus for exposing a radiation-sensitive substrate arranged in the region of an image plane of a projection lens to at least one image of a pattern of a mask arranged in the region of an object plane of the projection lens, comprising: a primary radiation source for emitting primary radiation having a working wavelength λ <260 nm ; an illumination system for receiving the primary radiation and for producing an illumination radiation directed onto the mask; and a projection lens for generating at least one image of the pattern in the region of the image surface of the projection lens, wherein the projection objective is configured according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and aspects of the invention will become apparent from the claims and from the following description of preferred embodiments of the invention, which are explained below with reference to the figures.

1 shows an embodiment of a DUV microlithography projection exposure apparatus;

2 shows a schematic meridional lens section of a first reference example in the form of a catadioptric projection lens with folded optical axis;

3 shows a meridional lens section through a projection lens according to a first embodiment with folded optical axis;

4 shows a meridional lens section through a projection lens according to a second embodiment with folded optical axis;

5 shows a meridional lens section through a projection lens according to a third embodiment with folded optical axis;

6 shows a meridional lens section through a projection lens according to a first embodiment with a straight optical axis;

7 shows a meridional lens section through a projection lens according to a second embodiment with straight optical axis;

8th shows a meridional lens section through a projection lens according to a third embodiment with straight optical axis.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description of preferred embodiments, the term "optical axis" refers to a straight line or a series of straight line sections through the centers of curvature of the optical elements. The optical axis can be folded at folding mirrors (deflecting mirrors) or other reflecting surfaces. The object in the examples is a mask (reticle) with the pattern of an integrated circuit, it can also be a different pattern, for example a grid. The image is projected in the examples onto a wafer provided with a photoresist layer, which serves as a substrate. Other substrates, such as liquid crystal display elements or optical grating substrates, are also possible.

In 1 An example of a microlithography projection exposure apparatus WSC is shown which can be used in the manufacture of semiconductor devices and other finely-structured components and works to achieve resolutions down to fractions of a micron with deep ultraviolet (DUV) electromagnetic radiation. The primary radiation source or light source LS is an ArF excimer laser with an operating wavelength λ of approximately 193 nm.

An illumination system ILL connected downstream of the light source LS generates in its exit surface ES a large, sharply delimited and substantially homogeneously illuminated illumination field, which is adapted to the telecentricity requirements of the projection objective PO arranged behind the light path. The illumination system ILL has facilities for setting different illumination modes (lighting settings) and can be switched, for example, between conventional on-axis illumination with different degree of coherence σ and off-axis illumination, wherein the off-axis illumination modes, for example, an annular illumination or Dipole illumination or quadrupole illumination or other multipolar illumination. The construction of suitable lighting systems is known per se and will therefore not be explained in detail here. The patent application US 2007/0165202 A1 (corresponding WO 2005/026843 A2 ) shows examples of lighting systems that can be used in various embodiments.

Those optical components which receive the light from the laser LS and form illumination radiation from the light which is directed onto the reticle M belong to the illumination system ILL of the projection exposure apparatus.

In the light path behind the illumination system, a device RS for holding and manipulating the mask M (reticle) is arranged such that the pattern arranged on the reticle lies in the object plane OS of the projection objective PO, which coincides with the exit plane ES of the illumination system and here also as the reticle plane OS is called. The mask is movable in this plane for scanner operation in a scan direction (y-direction) perpendicular to the optical axis OA (z-direction) by means of a scan drive.

Behind the reticle plane OS follows the projection objective PO which acts as a reduction objective and an image of the pattern arranged on the mask M on a reduced scale, for example at a scale of 1: 4 (| β | = 0.25) or 1: 5 (| β | = 0.20 ) is imaged onto a substrate W coated with a photoresist layer or photoresist layer whose photosensitive substrate surface SS lies in the region of the image plane IS of the projection objective PO.

The substrate to be exposed, which in the example is a semiconductor wafer W, is held by a device WS comprising a scanner drive to move the wafer in synchronism with the reticle M perpendicular to the optical axis OA in a scanning direction (y direction). to move. The device WS, which is also referred to as "wafer days", and the device RS, which is also referred to as "reticle days", are part of a scanner device which is controlled via a scan control device, which in the embodiment is transferred to the central control device CU the projection exposure system is integrated.

The illumination field generated by the illumination system ILL defines the effective object field OF used in the projection exposure. This is rectangular in the example case, has a parallel to the scanning direction (y-direction) measured height A * and a perpendicular thereto (in the x-direction) measured width B *> A *. The aspect ratio AR = B * / A * is generally between 2 and 10, in particular between 3 and 6. The effective object field is located at a distance in the y-direction next to the optical axis (off-axis field or off-axis field). The effective image field optically conjugate to the effective object field in the image area IS has the same shape and aspect ratio between height B and width A as the effective object field, but the absolute field size is reduced by the magnification β of the projection objective, i. H. A = | β | A * and B = | β | B *.

2 shows a schematic meridional lens section of a first reference example in the form of a catadioptric projection lens REF1 with selected beams to illustrate the imaging beam path of the running through the projection lens projection radiation. The reference example is not constructed according to the claimed invention. It is used here for comparison purposes.

The projection objective is provided as a reduction-acting imaging system for imaging a pattern of a mask arranged in its object plane OS on a reduced scale, for example on a scale of 4: 1, onto its image plane IS aligned parallel to the object plane. In this case, exactly two real intermediate images IMI1, IMI2 are generated between the object plane and the image plane. A first (dioptric) objective part OP1 constructed exclusively with transparent optical elements and therefore refractive (dioptric) is designed such that the pattern of the object plane is imaged into the first intermediate image IMI1 essentially without any change in size. A second, catadioptric objective part OP2 images the first intermediate image IMI1 onto the second intermediate image IMI2 essentially without any change in size. A third, purely refractive objective part OP3 is designed to image the second intermediate image IMI2 into the image plane IS with great reduction.

Between the object plane and the first intermediate image, between the first and the second intermediate image and between the second intermediate image and the image plane, there are respective pupil surfaces P1, P2, P3 of the imaging system where the main beam CR of the optical image intersects the optical axis OA. In the area of the pupil surface P3 of the third objective part OP3, the aperture stop AS of the system is attached. The pupil surface P2 within the catadioptric second objective part OP2 is in the immediate vicinity of a concave mirror CM.

If the projection objective is designed and operated as an immersion objective, then during operation of the projection objective, a thin layer of immersion liquid, which is located between the exit face of the projection objective and the image plane IS, is transmitted. Immersion lenses with a comparable basic structure are z. In the international patent application WO 2004/019128 A2 shown. In immersion mode, image-side numerical apertures NA> 1 are possible. A configuration as a dry objective is also possible, here the image-side numerical aperture is limited to values NA <1.

The catadioptric second objective part OP2 contains the single concave mirror CM of the projection objective. Immediately before the concave mirror is a negative group NG with two negative lenses L2-2 and L2-3. In this arrangement, sometimes called Schupmann achromat, the Petzvalkorrektur, d. H. the correction of the field curvature, by the curvature of the concave mirror and the negative lenses in the vicinity, the chromatic correction achieved by the refractive power of the negative lenses in front of the concave mirror and the diaphragm position with respect to the concave mirror.

A reflective deflection device serves to separate the beam bundle extending from the object plane OS to the concave mirror CM or the corresponding partial beam path from the beam bundle or partial beam path that runs after reflection at the concave mirror between it and the image plane IS. For this purpose, the deflecting device has a plane first deflecting mirror FM1 for reflecting the radiation coming from the object plane to the concave mirror CM and a second deflecting mirror FM2 aligned at right angles to the first deflecting mirror FM1 and reflecting the radiation reflected by the concave mirror Direction image plane IS redirects. Since the optical axis is folded at the deflecting mirrors, the deflecting mirrors in this application are also referred to as folding mirrors. The deflecting mirrors are tilted with respect to the optical axis OA of the projection lens about tilting axes extending perpendicular to the optical axis and parallel to a first direction (x-direction), e.g. B. by 45 °. In a design of the projection objective for the scanning operation, the first direction (x-direction) is perpendicular to the scanning direction (y-direction) and thus perpendicular to the direction of movement of the mask (reticle) and substrate (wafer). For this purpose, the deflection device is realized by a prism, the outside of which mirrored, perpendicularly aligned catheter surfaces serve as deflecting mirrors.

The intermediate images IMI1, IMI2 are in each case in the optical proximity of their closest folding mirrors FM1 and FM2, but have an optical distance to them, so that any errors on the mirror surfaces are not sharply imaged in the image plane and the plane deflection mirror (plane mirror) FM1 , FM2 are in the range of moderate radiation energy density.

The positions of the (paraxial) intermediate images define field levels of the system which are optically conjugate to the object plane or to the image plane. The deflection mirrors are in optical proximity to field levels of the system, which is also referred to as "close to field" in the context of this application. In this case, the first deflecting mirror is arranged in the optical proximity of a first field plane belonging to the first intermediate image IMI1 and the second deflecting mirror is arranged in optical proximity to a second field plane which is optically conjugate to the first field plane and belongs to the second intermediate image IMI2.

The optical proximity or the optical distance of an optical surface to a reference plane (eg a field plane or a pupil plane) is described in this application by the so-called subaperture ratio SAR. The subaperture ratio SAR of an optical surface is defined as follows for the purposes of this application: SAR = sign h (r / (| h | + | r |)) where r denotes the marginal ray height, h the principal ray height and the sign function sign x denotes the sign of x, where by convention sign 0 = 1. Under main beam height, the beam height of the main beam of a field point of the object field is understood with absolute maximum field height. This field point is usually given by the field ceiling, it can be rotated by a mental rotation in the plane of the drawing. Then the beam height is signed. The term "edge beam height" is understood to mean the beam height of a beam with maximum aperture starting from the point of intersection of the optical axis with the object plane. This field point does not have to contribute to the transmission of the pattern arranged in the object plane, especially in the case of off-axis image fields.

In particular, in the folded designs, the outer beam shown is not the beam of the outermost, rotated in the plane of the drawing field point, but the beam of the upper field edge. Therefore, a graphic determination of the subaperture ratio is not possible for the folded designs.

The situation is different with the presentation of the inline design. Here, the outermost field point represented represents the field ceiling rotated in the plane of the drawing. Thus, the subaperture ratio can be determined graphically on these representations.

The subaperture ratio is a signed quantity, which is a measure of the field or pupil near a plane in the beam path. By definition, the subaperture ratio is normalized to values between -1 and +1, where the subaperture ratio is zero at each field level, and at a pupil level, the subaperture ratio jumps from -1 to +1 or vice versa. An absolute subaperture ratio of 1 thus determines a pupil plane.

An optical surface or plane is now referred to as "(optically) close" to an optical reference surface if the subaperture ratios of these two surfaces are comparable in numerical value.

In particular, an optical surface or a plane is referred to as "near (optically) close to the field" if it has a subaperture ratio which is close to 0. An optical surface or a plane is referred to as "close to the pupil" if it has a subaperture ratio which is close to 1 in terms of magnitude.

For both deflection mirrors, it is true that no optical element is disposed between the deflection mirror and the nearest intermediate image (immediate proximity) and that the subaperture ratio SAR is less than 0.3, in particular less than 0.2, in terms of magnitude.

The deflecting mirrors are therefore referred to as (optically) close to the field

In the field of microlithography lenses and other transparent optical elements are usually supported by a plurality of holding elements, which are arranged uniformly on the circumference of the respective optical element. The optical element has an optical useful region lying in the imaging beam path (projection beam path) and an edge region lying outside the optical useful region, wherein one or more holding elements of the holding device associated with the optical element act on the edge region. In the optical useful range, the surfaces of the optical element are prepared with optical quality, while in the edge region, the optical quality does not have to be achieved. The size of the optical payload is often indicated by the "free optical diameter" of the optical element. According to another formulation, the optically free diameter or the free optical diameter is understood to be the diameter of the circle which is centered on the optical axis and circumscribes with minimal diameter all the light beams contributing to the imaging.

The optical structure can be characterized as follows. The first objective part OP1 can be subdivided into two immediately successive lens groups LG1-1 and LG1-2, which each have a total positive refractive power in order to form the first intermediate image IMI1 from the beam bundles diverging from the object field points. The first lens group LG1-1 comprises all lenses between the object plane and the first pupil surface P1, the second lens group LG1-2 comprises all lenses between the first pupil surface and the first intermediate image IMI1. To the first lens group belong in this order from the object side to the image side a concave to the object concave weak positive meniscus lens L1-1 with aspherical entrance surface and spherical exit surface, a concave positive meniscus lens L1-2 with spherical entrance surface and aspherical exit surface, a strong positive acting to the object side third lens L1-3 with spherical entrance surface and strongly aspherized exit surface, a positive meniscus lens L1-4 with convex spherical entry surface and concave spherical exit surface, a substantially refractive power free plan plate PP and a subsequent weak positive meniscus lens L1-5 with concave entrance side and convex Exit side immediately at the first pupil surface.

The first lens of the second lens group LG1-2 is a negative meniscus lens L1-6 concave to the first pupil surface and having a concave spherical entrance side and an aspherical exit side. This is followed by a positive meniscus lens L1-7 concave spherical entrance side and spherical exit side concave to the first pupil surface, another positive meniscus lens with spherical entrance side and spherical exit side concave to the first pupil surface, a biconvex positive lens L1-8 and a positive concave meniscus lens on the image side L1-9 with aspherical entry surface and spherical exit surface.

The second objective part OP2 comprises the single concave mirror CM of the projection objective at the second pupil surface and the two negative lenses L2-1 and L2-2 of the negative group NG arranged directly in front of it, which together with the concave mirror CM form a Schupmann achromat and the first intermediate image IMI1 in FIG depict the second intermediate IMI2.

The third objective part OP3 can be subdivided into four successive lens groups having the refractive power sequence positive-negative-positive-positive and P-N-P-P, respectively. The first lens group LG3-1 of the third objective part immediately following the second intermediate image has four lenses, overall positive refractive power and serves to deflect the main beams from a non-telecentric second intermediate image IMI2 in the pupil position direction (third pupil surface P3). The marginal rays are collimated. For this purpose, there is a biconvex positive lens L3-1 with spherical entrance side and aspherical exit side following directly onto the second intermediate image, a subsequent further biconvex positive lens L3-2 with spherical entrance side and spherical exit side, a positive concave meniscus lens L3-3 with spherical entry side and exit sides, and another image side concave positive meniscus lens L3-4 with spherical inlet side and outlet side.

The immediately following second lens group LG3-2 has negative refractive power and serves for diverging the marginal rays in order to be able to produce a large pupil diameter in the subsequent third pupil surface. For this purpose, this lens group has two negative lenses, namely a biconcave negative lens L3-5 with aspheric inlet side and spherical exit side and another biconcave negative lens L3-6 with spherical inlet side and outlet side.

The negative group L3-2 is followed by a positive third lens group LG3-3 with five lenses between the negative group LG3-2 and the third pupil surface. The third lens group LG3-3 includes an object-side concave negative meniscus lens L3-7 having a spherical entrance side and an aspherical exit side, an object-side concave meniscus lens L3-8 having an aspheric entrance side and a spherical exit side, another positive meniscus lens L3-9 having an aspherical entrance side and a spherical one Exit side, a biconvex positive lens L3-10 with spherical entrance side and strong aspherical exit side as well as another biconvex positive lens L3-11 with spherical entrance side and strongly aspherical exit side.

Between the aperture diaphragm AS and the image plane IS lying on the third pupil surface P3, there follows a further positive group LG3-4 whose essential function is to combine the beam bundles from the large pupil diameter at the aperture diaphragm to produce a high image-side numerical aperture NA. For this purpose, this lens group contains a positive meniscus lens L3-12 with a spherical inlet side and aspherical outlet side facing the aperture diaphragm, a further positive meniscus lens L3-13 with a spherical inlet side and aspherical outlet side, and a plano-convex positive lens with a spherical, strongly curved inlet surface and a planar outlet surface , This lens forms the last lens LL of the projection lens immediately in front of the image plane IS.

The projection objective has two so-called waist groups, namely a first waist group TG1 within the first objective part OP1 and a second waist group TG2 within the third objective part OP3. Within the waist groups, there is in each case a local constriction E of the projection beam path with a local minimum of the cross section of the projection beam path.

Within the first objective part OP1, there is a local constriction E of the projection beam path in the transition region between the first lens group LG1-1 and the second lens group LG1-2. The optical elements in the region of this constriction or waist and in the areas immediately adjacent to the object side and the image side form the first waist group TG1. The first waist group includes all lenses L1-4 to L1-8 disposed between an object-side first boundary lens G1-1 (corresponding to lens 1-3) and an image-side second boundary lens G1-2 (corresponding to L1-8). The first waist group also includes the plane-parallel plate PP. As apparent from Table 2, the free optical diameter of each of the lenses of the waist group is smaller than the smaller one of the free optical diameters of the first boundary lens G1-1 and the second boundary lens G1-2. The border lenses are also recognizable by the fact that the free optical diameters of the lenses on both sides of each boundary lens are smaller than the optical free diameters of the respective boundary lenses. A boundary lens thus marks a local maximum of the free optical diameter. The first waist group TG1 includes the position of the first pupil surface P1 and extends to both sides of this first pupil surface.

The second waist group TG2 within the third objective part OP3 contains the local constriction of the production beam path in the region of the biconcave negative lenses L3-5 and L3-6, where there is a local minimum of the cross section of the projection beam path in the third objective part. The second waist group TG2 is enclosed on the object side by the first boundary lens G3-1 (corresponding to L3-2) and on the image side by the second boundary lens G3-2 (corresponding to L3-10). The second waist group TG2 thus includes the lenses L3-3 to L3-9. The constriction in the beam path is located in an intermediate region optically between the second intermediate image (a field plane) and the third pupil surface P3.

The sequence of lenses described here also applies to the first three exemplary embodiments described below (FIG. 3 to 5 ).

As can be seen from Table 2, there are all the lenses and the parallel plate PP, so all transparent optical elements of the projection lens of synthetic quartz glass (fused silica) which is 193 nm has a refractive index of about n _SiO2 = 1:56 at the operating wavelength. It is an immersion objective which, when using water as the immersion liquid between the last lens LL and the image plane IS, has an image-side numerical aperture of NA = 1.35.

It has been recognized that in such optical imaging systems, problems with radiation-induced lens heating may occur, especially in certain lenses and / or in particular lighting settings. For example, extreme, ie very coherent, dipole settings can lead to very punctual, ie locally highly concentrated, heat loads on the lenses, especially in those areas corresponding to the dipole-like illumination intensity distribution in the pupil plane of the upstream illumination system, in particular in near-pupil lenses. Where pupil-close lenses tend to have small optical clear diameters, the illuminance levels are correspondingly higher. For In addition, the lenses of the first objective part OP1 are considered to still be relatively close to the object plane of the projection lens, where overall there is still a greater overall light flux than at a greater distance from the object plane, for example in the second or third objective part.

When lenses near the pupil are heated with a dipole-like illumination, essentially a slit heats up across the lens. This can lead to field-constant defocus and astigmatism in the lowest order. While the defocus can be relatively easily compensated by appropriate manipulations, such as axial displacement of the substrate, this is not or only to a limited extent for the astigmatism.

Substantial improvements compared to the reference design (projection lens REF1) can be achieved if some or all of the lenses especially affected by inhomogeneous "lens heating" are not made of quartz glass but of suitable fluoride crystal material, for example calcium fluoride (CaF ₂ ).

In 3 is illustrative of a meridional lens cut through a projection lens 300 shown according to a first embodiment. Compared to the first reference system 1 Here are the three lenses arranged in the immediate vicinity of the first pupil surface L1-4, L1-5 and L1-6 and arranged between the lenses L1-4 and L1-5 plan plate PP have been replaced by correspondingly designed optical elements made of calcium fluoride (fluorspar) , Fluoride crystal lenses and other fluoride crystal material optical elements are indicated by hatching.

Thus, the first waist group TG1, in which the local constriction E of the projection beam path is located at the first pupil surface P1, has four immediately successive fluoride crystal material optical elements, namely the three fluoride crystal lenses L1-4, L1-5 and L1-6, and the transparent face plate PP , In other words, the first waist group has three contiguous refracting optical elements made of fluoride crystal material, namely, the three fluoride crystal lenses L1-4, L1-5 and L1-6. The optical position of the fluoride crystal lenses is characterized by a Subaperturdurchmesser SAR in the range of magnitude greater than 0.3.

The fluoride crystal lenses or the fluoride crystal plate are those optical elements having the smallest free optical diameters within the first waist group. Immediately before the image plane next fluoride crystal lens L1-4 is the quartz glass lens L1-3, so the first boundary lens G1-1, which has a concave to the fluoride crystal lenses exit surface. Immediately behind the image plane of the next fluoride crystal lens L1-6 of the first waist group is the quartz glass lens L1-7 which is part of the first waist group and has a concave entrance surface facing the fluoride crystal lenses. The framing of the fluoride crystal elements between quartz glass lenses with the fluoride crystal lenses facing concave surfaces is favorable for beam guidance with relatively low incidence angles. Further, it can be seen that the first waist group TG1 has two quartz glass lenses (L1-7 and L1-8) in addition to the four fluoride crystal material optical elements, but the number of fluoride crystal elements is larger than that of the quartz glass elements, namely, twice as large in the example.

After replacement of the near-pupil-arranged relatively small diameter optical elements by fluorspar elements (optical elements made of calcium fluoride), these optical elements heat up almost as well as corresponding optical elements of quartz glass, possibly due to the slightly lower absorption of calcium fluoride compared to quartz glass an absorption induced heating may be slightly lower. In any case, however, due to the significantly higher specific thermal conductivity of calcium fluoride, the heat generated in the particularly strongly irradiated areas is distributed much faster and better over the entire lens or the entire plane plate, so that the astigmatism and possibly other aberrations induced by inhomogeneous lens heating are very high are much smaller than in the case of using quartz glass lenses in a waist group. This significantly reduces the level of heat-induced aberrations.

The following information applies to the order of magnitude of the thermal conductivities of some of the materials of interest here (figures in each case in [W / (mK)] at 20 ° C.): SiO ₂ (quartz glass): 1.38; CaF ₂ : 9.71; BaF ₂ : 11.7; LiF: 4.0.

In 4 is a meridional lens section of another embodiment of a projection lens 400 shown, can be achieved by targeted use of fluoride crystal material as a substitute for quartz glass material, an improvement of the lens-heating behavior. The first objective part OP1 and the second lens part OP2 have comparable structure to the embodiment of 3 , In particular, here too, in the first objective part OP1, a first waist group TG1 with four successive optical elements made of fluoride crystal material is arranged in the region around the first pupil surface P1.

In the embodiment of 4 are in addition to these lenses compared to the embodiment of 3 two more quartz glass lenses have been replaced by fluoride crystal lenses made of calcium fluoride, namely the two biconcave negative lenses L3-5, L3-6 within the third lens part OP3. These lenses are not in optical proximity to the nearest pupil surface (third pupil surface P3 with aperture stop AS), but in an intermediate region between the second intermediate image IMI2 and the subsequent third pupil surface P3. The optical position of the fluoride crystal lenses is characterized by a subaperture diameter SAR in the range between 0.3 and 0.7. Although these lenses are much more homogeneously illuminated due to the optical distance to the nearest pupil surface, for example in a dipole illumination setting than lying closer to the pupil surface, they still experience relatively strong heating by the projection radiation due to their relatively small free optical diameter. Therefore, it can be assumed that these lenses also contribute a non-negligible proportion to the aberration level caused by lens heating.

These two negative lenses, with the exception of the last lens LL, are the lenses with the smallest optical free diameter within the third objective part OP3. In particular, the optical free diameters of the two fluoride crystal lenses are each smaller than the optical free diameters of the immediately preceding positive meniscus lens L3-4 and the image immediately downstream negative meniscus lens L3-7, each belonging to the second waist group TG2 and made of quartz glass.

It is noteworthy that a quartz glass lens L3-4 with a concave exit surface is arranged immediately before the fluoride crystal lens L3-5 of the second waist group TG2 closest to the object surface, and that a quartz glass lens L3-7 with immediately behind the image surface next fluoride crystal lens L3-6 of the second waist group a concave entrance surface is arranged.

In 5 is a meridional lens section through another embodiment of a projection lens 500 in which fluoride crystal lenses are substituted for quartz glass lenses to reduce sensitivity to lens heating. The first objective part OP1 and the third objective part OP3 correspond in structure to the corresponding objective parts of the second embodiment ( 4 ), ie with in each case at least two immediately successive fluoride crystal lenses in the waist regions, where there is a local constriction of the projection beam path in the first and third objective part.

In the embodiment of 5 Finally, the double-penetrated, close to the pupil arranged negative lenses L2-1 and L2-2 are formed immediately before the concave mirror as fluoride crystal lenses. Although these lenses are relatively large in terms of their free optical diameter, so that spreads the illumination intensity on a relatively large area, but by the double passage of the projection light, they experience a relatively high radiation exposure, which contributes to a relatively strong Lens-heating contribution with the above consequences (including constant astigmatism).

It would be possible to replace one or more lenses in the vicinity of the third pupil surface P3 by corresponding lenses made of a fluoride crystal material for further reduction of lens heating effects. However, due to the limited availability of sufficiently large fluoride crystal material blocks of suitable optical quality, this can be done e.g. B. be omitted for cost reasons.

In the following embodiments, the considerations and principles underlying the claimed invention are applied to another type of catadioptric projection lenses, namely those in which all the optical elements are arranged along a straight, unfolded optical axis. As a reference system for comparison purposes, the (not pictorially shown) projection lens of the 3 out US 2008/0174858 A1 by the applicant, the disclosure of which is hereby made by reference to the content of the present description. In the reference system, all transparent optical elements are made of quartz glass.

6 shows an embodiment of a catadioptric projection lens 600 , which is designed as an immersion objective for a working wavelength of about 193 nm. It is intended to image a pattern of a mask arranged in its object plane OS on a reduced scale, for example on a scale of 4: 1, onto its image plane IS aligned parallel to the object plane. In this case, exactly two real intermediate images IMI1, IMI2 are generated between the object plane and the image plane. A first, refractive (dioptric) Lens part OP1 is designed so that the pattern of the object plane is imaged on a larger scale in the first intermediate image IMI1. A second, reflective (catoptric) objective part OP2 images the first intermediate image IMI1 into the second intermediate image IMI2 essentially without any change in size (magnification approx. 1: 1). A third, refractive (dioptric) objective part OP3 is designed to image the second intermediate image IMI2 into the image plane IS with great reduction. In this case, during operation of the projection objective, a thin layer of an immersion liquid IM is irradiated, which is located between the exit surface of the projection objective and the image plane IS.

The catoptric second objective part OP2 consists of a first concave mirror CM1 with a concave mirror surface facing the object plane OS and a second concave mirror CM2 with a concave mirror surface facing the image plane IS. The regions of the aspheric mirror surfaces of both mirrors used for imaging or reflection are connected in one another, ie. H. they have no holes or holes, so that no obscuration effects occur during the reflection. Each of the mirror surfaces of the concave mirrors defines a curvature surface, which is a mathematical surface that extends beyond the edges of the physical mirror surfaces and contains that mirror surface. The first and second mirror surfaces are parts of rotationally symmetric curvature surfaces with a common axis of symmetry, which coincides with the coaxially arranged optical axes of the first objective part OP1 and the third objective part OP3. Therefore, the entire projection lens is rotationally symmetric and has a single, straight, unfolded optical axis OA that is common to all refractive and reflective optical components.

The mutually facing mirror surfaces of the concave mirrors CM1, CM2 define a catadioptric cavity in the axial direction. The intermediate images IMI1, IMI2 are both within this catadioptric cavity, wherein at least the paraxial intermediate images lie in the middle region between the concave mirrors with a relatively large optical distance to them. The concave mirrors have relatively small diameters, their optically used areas lie on different sides of the optical axis OA and are obliquely illuminated off-axis. The imaging beam path extending from the object plane to the image plane passes the mirror edges facing the optical axis in each case without vignetting.

Between the object plane and the first intermediate image, between the first and the second intermediate image and between the second intermediate image and the image plane, there are respective pupil surfaces P1, P2 and P3 of the imaging system where the main beam CR of the optical image intersects the optical axis. The pupil area P2 within the catadioptric second objective part is at a relatively large optical distance from the concave mirrors CM1, CM2 in the central area of the catadioptric cavity so that all concave mirrors are optically distant from a pupil area in a region where the main beam height of the image is the marginal beam height of the image exceeds. In the area of the pupil surface P3 of the third objective part OP3, the aperture stop AS of the system is attached.

The optical structure can be characterized as follows. The first objective part OP1 can be subdivided into two directly successive lens groups LG1-1 and LG1-2, each of which has a total positive refractive power, in order to form the first intermediate image IMI1 from the beams divergent from the object field points. The first lens group comprises all lenses between the object plane and the first pupil surface P1, and the second lens group LG1-2 comprises all lenses between the first pupil surface and the first intermediate image IMI1. To the first lens group belong in this order from the object side to the image side a biconvex positive lens L1-1 with spherical entrance side and aspherical exit side, a image side concave negative meniscus lens L1-2 with spherical entry and exit side, a positive concave meniscus lens L1- 3 with spherical entrance and exit side, a positive lens L1-4 with strongly aspherized entrance surface and spherical exit surface, a positive lens L1-5 with almost flat entrance surface and aspherical exit surface, a plane-parallel plate PP1 and an object-side concave positive meniscus lens L1-7. The second lens group LG1-2 consists of three relatively thin optical elements, namely a plane plate PP2, a bilaterally spherical, object-side concave positive meniscus lens L1-7 and a concave to the object side meniscus lens L1-8 immediately before the first intermediate image IMI1.

The third objective part OP3 can be subdivided into four successive lens groups with the power sequence positive-negative-positive-positive and P-N-P-P, respectively.

The first lens group LG3-1 of the third objective part immediately following the second intermediate image has two lenses L3-1, L3-2 and overall positive refractive power in order to collect the beams coming from the second intermediate image.

The subsequent second lens group LG3-2 has negative refractive power and contributes to the diverging of the marginal rays in order to be able to produce a large pupil diameter in the subsequent third pupil surface. For this purpose, this lens group has two negative lenses, namely a concave image-side, bilaterally spherical negative meniscus lens L3-3 and a biconcave negative lens L3-4 with aspheric entrance surface and spherical exit surface.

The negative group L3-2 is followed by an overall positive third lens group LG3-3 with six lenses between the negative group LG3-2 and the third pupil area P3. The third lens group LG3-3 includes an image side concave positive meniscus lens L3-5 with aspheric entrance surface and spherical exit surface, an object side concave negative meniscus lens L3-6 with spherical entrance side and aspherical exit side, a biconvex positive lens L3-7 with aspherical entrance side and spherical Exit side, a positive meniscus lens L3-8 with aspheric entrance side and spherical exit side, a positive lens L3-9 with strong aspherical entrance surface and the image side convex, spherical exit surface and a biconvex positive lens L3-10 with spherical entrance surface and aspheric exit surface immediately adjacent to the third pupil surface P3.

Between the aperture diaphragm AS lying on the third pupil surface P3 and the image plane IS, there follows a further positive group LG3-4, which essentially contributes to the generation of the high image-side numerical aperture NA. This fourth lens group contains only three positive lenses, namely a biconvex positive lens L1-11 with spherical entrance side and aspherical exit side, a positive lens L1-12 with spherically curved entrance surface and strongly aspherical exit surface and a plano-convex positive lens LL with spherical, strongly curved entrance surface and flat exit surface. This lens forms the last lens LL of the projection lens immediately in front of the image plane.

The sequence of lenses described here also applies to the two exemplary embodiments described below (US Pat. 7 and 8th ).

As can be seen from Table 6, all lenses of the projection lens except for three optical elements 600 made of synthetic quartz glass. One exception is the three optical elements L1-5, PP1 and L1-6 arranged in front of the first pupil surface P1, which are indicated by hatching. These consist of a fluoride crystal material, namely calcium fluoride. The first objective part OP1 thus has a first waist group TG1 with three contiguous optical elements of a crystalline fluoride material, while all other optical elements are made of quartz glass. The first waist group TG1 is included on the object side by the first boundary lens G1-1 (corresponding to L1-3) and on the image side by the second boundary lens G1-2 (corresponding to L1-8). The three fluoride crystal elements are the optical elements with the smallest free optical diameters of this waist group. There is no negative lens in this waist group, especially no negative lens of fluoride crystal material.

The positive influence on the lens heating behavior of the projection objective is basically similar to that in connection with the first embodiment of FIG 3 described. The three fluoride crystal elements are located in the region of relatively small beam diameter, which follows directly on the object plane and is therefore exposed to a particularly high flux of light. In extreme lighting settings, such as dipole illumination, highly inhomogeneous illumination intensity distributions can occur, which can lead to difficult to correct aberrations, in particular astigmatism. Due to the significantly higher specific thermal conductivity of calcium fluoride compared to quartz glass, a much more homogeneous heat distribution than in comparable quartz glass lenses results, whereby the level of heat-induced aberrations compared to the same system can be reduced with quartz glass lenses.

In 7 is a meridional lens section of another embodiment of a projection lens 700 which has the same structure as the embodiment in terms of the sequence and shape of lenses and other optical elements 6 , In contrast, however, all the lenses of the first objective part OP1 are quartz glass lenses. Another difference is that in the area of the constriction of the projection beam path within the third lens part OP3 within the second waist group TG2, three of the quartz glass lenses, namely the lenses L3-3, L3-4 and L3-5, are replaced by fluoride crystal lenses of essentially the same shape are. This makes it possible to reduce heat-induced aberrations that could be caused by lens heating in the region of the second constriction compared to the use of quartz glass lenses in this area. Also, this embodiment thus has a waist group (second waist group TG2) with three immediately successive fluoride crystal lenses, this waist group is located in the third objective part OP3. The second waist group becomes the object side by the first boundary lens G3-1 (corresponding to L3-1) and image side by the second boundary lens G3-2 (corresponding to L3-9).

8th shows a meridional lens section through another embodiment of a catadioptric in-line projection lens, which has the same structure in terms of the nature and sequence of lenses and other optical elements as the embodiments of the 6 and 7 , The embodiment is characterized in that here two waist groups are provided, each containing at least one fluoride crystal lens. Specifically, the first waist group TG1, which is located in the area of the first pupil surface P1 of the first objective part OP1, has three immediately successive fluoride crystal elements, and the second waist group TG2, which is located in an intermediate region between the second intermediate image IMI2 and the third pupil surface P3, within the third lens part OP3, in each case three immediately successive fluoride crystal lenses. It can be seen that this construction with waist groups in two spatially separate areas of relatively large radiation exposure, a reduction of the Lens Heating problem can be achieved by the use of fluoride crystal material.

In the illustrated embodiments, the fluoride crystal lenses and the other fluoride crystal material optical elements are each made of calcium fluoride. In principle, other crystalline materials, such as, for example, barium fluoride or lithium fluoride, are also suitable for the reduction of lens heating problems, in particular because they have a significantly improved thermal conductivity compared with amorphous quartz glass.

It can be seen that in these examples, the first waist group TG1 in the first lens part does not contain negative lenses but a pupil (first pupil surface). In contrast, there is no pupil area in the region of the second waist group TG2 of the third objective part, but this waist group contains at least one negative lens (two negative lenses in the example).

The specifications of the projection lenses shown in the drawing figures are given in the tables summarized at the end of the description, the numbering of each of which corresponds to the numbering of the corresponding drawing figure.

The tables summarize the specification of each design in tabular form. Where column "SURF" gives the number of a refracting or otherwise marked surface, column "RADIUS" the radius r of the surface (in mm), column "THICKNESS" the distance d called the thickness of the surface to the following surface (in mm) and column "MATERIAL" the material of the optical components. Columns "INDEX1", "INDEX2" and "INDEX3" 5 indicate the refractive index of the material at the design operating wavelength 193.3 nm (INDEX1) as well as 192.8 nm (INDEX2) and 193.8 (INDEX3). The column "SEMIDIAM" indicates the usable, free radii or half the free optical diameters of the lenses (in mm) or the optical elements. The radius r = 0 (in the column "RADIUS") corresponds to one level. Some optical surfaces are aspherical. Tables with the suffix "A" indicate the corresponding aspherical data, whereby the aspheric surfaces are calculated according to the following rule: p (h) = [((1 / r) h ²⁾ / (1 + SQRT (1 - (1 + K) (1 / r) ² H ^2))] + C1 · h ⁴ + C 2 · h ⁶ + ....

The reciprocal (1 / r) of the radius indicates the area curvature and h the distance of a surface point from the optical axis (ie the beam height). Thus, p (h) gives the arrow height, i. H. the distance of the surface point from the surface apex in the z-direction (direction of the optical axis). The constants K, C1, C2, ... are given in the tables with the suffix "A".

Tabelle 2A (M241A)

Tabelle 3 (M269A)

Tabelle 3A (M269A)

Tabelle 4 (M270A)

Tabelle 4A (M270A)

Tabelle 5 (M271A)

Tabelle 5A (M271A)

Tabelle 6 (M412)

Tabelle 6A (M412)

Tabelle 7 (M413)

Tabelle 7A (M413)

Tabelle 8 (M414)

Tabelle 8A (M414)

All projection lenses of the exemplary embodiments are designed as immersion objectives with a numerical aperture NA = 1.35 on the image side, wherein water is used as the immersion liquid. The object height is 61.5 mm in each case in the embodiments with the folded optical axis, and 63.5 mm in the embodiments with a straight optical axis (in-line systems) in each case. Table 2 (M241A)

Table 2A (M241A)

Table 3 (M269A)

Table 3A (M269A)

Table 4 (M270A)

Table 4A (M270A)

Table 5 (M271A)

Table 5A (M271A)

Table 6 (M412)

Table 6A (M412)

Table 7 (M413)

Table 7A (M413)

Table 8 (M414)

Table 8A (M414)

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2006/0077366 A1 [0009]
• WO 2004/019128 A1 [0009]
• US 7362508 B2 [0009]
• EP 1480065 A2 [0009, 0013]
• WO 2005/069055 A2 [0010, 0013]
• US 2005/0248856 A1 [0011]
• US 2009/0316256 A1 [0012]
• US 2007/0165202 A1 [0057]
• WO 2005/026843 A2 [0057]
• WO 2004/019128 A2 [0066]
• US 2008/0174858 A1 [0107]

Claims (23)

Catadioptric projection objective (PO) for imaging a pattern of a mask arranged in an object field of an object surface (OS) of the projection objective into an image field arranged in the image surface (IS) of the projection objective by means of electromagnetic radiation having a working wavelength λ <260 nm with: a plurality of lenses comprising a plurality of quartz glass lenses and at least one fluoride crystal lens; and at least one concave mirror (CM); in which: the lenses form at least one waist group (TG1, TG2) containing a local constriction (E) of a projection beam path having a local minimum of the cross-section of the projection beam path; the waist group (TG1, TG2) includes all the lenses disposed between an object-side first boundary lens (G1-1, G3-1) and an image-side second boundary lens (G1-2, G2-2), a free optical diameter of each of the lenses of the waist group (TG1, TG2) is smaller than a minimum of the free optical diameters of the first boundary lens (G1-1, G3-1) and the second boundary lens (G1-2, G3-2), and the waist group (TG1, TG2) has at least one fluoride crystal lens. A projection lens according to claim 1, wherein the waist group (TG1, TG2) comprises at least two immediately successive fluoride crystal lenses. A projection lens according to claim 1 or 2, wherein the waist group (TG1, TG2) comprises at least one negative power fluoride crystal lens (L1-6, L3-4, L3-5). A projection lens according to any one of the preceding claims, wherein the waist group (TG2) comprises at least two immediately successive negative refractive index fluoride crystal lenses (L3-4, L3-5). A projection lens according to any one of the preceding claims, wherein the waist group (TG2) comprises at least one biconcave negative lens (L3-5, L3-6) of a crystalline fluoride material. A projection lens according to any one of the preceding claims, wherein the first boundary lens (G1-1, G3-1) and / or the second boundary lens (G1-2, G3-2) is a quartz glass lens. A projection lens according to any one of the preceding claims, wherein the first boundary lens (G1-1, G3-1) and / or the second boundary lens (G1-2, G3-2) is a positive lens. Projection objective according to one of the preceding claims, wherein immediately before one of the object surface (OS) nearest fluoride crystal lens (L1-4) of a waist group (TG1) a quartz glass lens (L1-3) is arranged with a concave exit surface and / or wherein immediately behind one of the image surface next to a fluoride crystal lens (L1-6) of a waist group (TG1), a quartz glass lens (L1-7) having a concave entrance surface is disposed. A projection lens according to any one of the preceding claims, wherein the fluoride crystal lenses (L1-4, L1-5, L1-6) of a waist group (TG1) are disposed between facing concave surfaces of immediately adjacent lenses (L1-3, L1-7). A projection lens according to any one of the preceding claims, wherein at least one of the boundary lenses (G1-1, G3-1, G1-2, G3-2) is a positive meniscus lens having a concave lens surface facing the waist group (TG1, TG2). Projection objective according to one of the preceding claims, wherein the projection objective ( 300 . 400 . 500 . 600 . 700 . 800 ) a first objective part (OP1) for imaging an object field in a first real intermediate image (IMI1), a second objective part (OP2) for generating a second real intermediate image (IMI2) with the radiation coming from the first objective part, and a third objective part (OP3 ) for imaging the second real intermediate image into the image plane (IS). A projection lens according to claim 11, wherein between the object surface (OS) and the first intermediate image (IMI1) there is a first pupil surface (P1) and a waist group (TG1) is arranged in the first objective part (OP1) such that the first pupil surface (P1) in the Range of the waist group (TG1) is located. A projection lens according to claim 12, wherein the waist group (TG1) comprises a substantially refractory transparent plate (PP) made of a crystalline fluoride material or quartz glass, the transparent plate (PP) being located immediately adjacent to the first pupil surface (P1). A projection lens according to claim 12 or 13, wherein the waist group (TG1) comprises at least three contiguous refractive power optical elements (L1-4, L1-5, L1-6) of a crystalline fluoride material. A projection lens according to claim 12, 13 or 14, wherein a third pupil surface (P3) is located between the second intermediate image (IMI2) and the image surface, and a waist group (TG2) is optically located in the third objective part (OP3) remote from the third pupil surface (P3) in that between the second intermediate image (IMI2) and the waist group (TG2) a plurality of synthetic quartz glass positive lenses and between the waist group (TG2) and the third pupil surface (P3) a plurality of synthetic quartz positive lenses are arranged. A projection lens according to claim 15, wherein said waist group (TG2) comprises two directly consecutive biconcave negative lenses (L3-5, L3-6; L3-3, L3-4) of a crystalline fluoride material. Projection objective according to one of the preceding claims, wherein the projection beam path has a first partial beam path extending between the object plane (OS) and the concave mirror (CM) and a second partial beam path extending between the concave mirror and the image plane (IS) and at least one negative lens (N2-1, N2-2) of a crystalline fluoride material is arranged in a double-penetrated region such that the first and the second partial beam path pass through the negative lens (N2-1, N2-2). A projection lens according to any one of the preceding claims, wherein the lenses comprise a last lens (LL) closest to the image plane, the last lens being of synthetic quartz glass. A projection lens according to any one of the preceding claims, wherein the crystalline fluoride material is calcium fluoride (CaF ₂ ). A projection lens according to any one of the preceding claims, wherein the projection objective comprises more quartz glass lenses than fluoride crystal lenses, with preferably more than 60% or more than 70% of all lenses being made of quartz glass. Projection exposure method for exposing a radiation-sensitive substrate to at least one image of a pattern of a mask, comprising the following steps: Providing a pattern between an illumination system and a projection objective of a projection exposure apparatus such that the pattern is arranged in the region of the object plane of the projection objective; Holding the substrate such that a radiation-sensitive surface of the substrate in the region of an object plane to the optically conjugate image plane of the projection lens is arranged; Illuminating an illumination region of the mask with an illumination radiation provided by the illumination system having an operating wavelength λ <260 nm; Projecting a part of the pattern located in the illumination area onto a field of view on the substrate with the aid of the projection objective, wherein all the beams of the projection radiation contributing to image formation in the image field form a projection beam path, wherein a projection lens according to any one of claims 1 to 20 is used. A projection exposure method according to claim 21, wherein in at least one exposure mode, multipolar illumination is used, in particular dipole illumination or quadrupole illumination. A projection exposure apparatus for exposing a radiation-sensitive substrate arranged in the region of an image surface of a projection lens to at least one image of a pattern of a mask arranged in the region of an object surface of the projection lens, comprising: a light source (LS) for emitting ultraviolet light having an operating wavelength λ <260 nm; an illumination system (ILL) for receiving the light of the light source and for forming illumination radiation directed to the pattern of the mask; and a projection objective (PO) for imaging the structure of the mask onto a photosensitive substrate; wherein the projection lens according to one of claims 1 to 20 is configured.

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